1. Field of the Invention
The invention relates to a centering and chucking system.
2. Description of Related Art
For machine tools in operation, it is frequently necessary to accurately fix an interchangeable element to a carrier body. For instance, an interchangeable spindle head (or another tool head) must be positioned very accurately on the frame or carriage of the machine tool to ensure that the spindle may take the desired position and that the tool may be moved exactly to the positions predetermined by the machine control. However, not only the tool or tool head supporting the tool (e.g. a spindle head) must be mounted in an exactly defined position and alignment, but the same is also applicable to the workpiece under treatment. If a workpiece is chucked on a pallet to be moved to a machine tool for machining the workpiece, the pallet must be positioned exactly at the machine tool so as to perform a machining by the tool precisely at the right point of the workpiece.
The known centering and chucking systems allow an exact positioning of the interchangeable element with respect to the carrier body in that the reference axes of carrier body and interchangeable element are coincident. However, difficulties may arise if the individual units of the machine tool are exposed to different temperatures. If a machine tool is tooled in the morning, in a cold factory, while, in the course of the day, temperature rises, the original centering conditions change. In other words, it may happen that the spindle of an interchangeable spindle head does not continue to occupy, relative to the machine tool, exactly the same position as taken originally and by which the machine program is dictated.
It has been known to connect, in the manner of a fixed bearing, one end of the interchangeable part (with round bolts) to the carrier body and to design the opposite end such as to form a displaceable loose bearing (with sword bolts), so that the interchangeable element may freely thermally change its length. In such a case, the only point of the interchangeable element which remains unchanged with respect to the carrier body is the site of the fixed bearing. Since the latter cannot be mounted in the reference axis where, in the case of a spindle head, for instance, the spindle is located, the reference axis (e.g. the spindle axis) is always spaced from the fixed bearing with resultant thermally conditioned changes of position of the reference axes of the two elements relative to each other.
According to U.S. Pat. No. 4,384,811, there has been known a milling machine comprising an interchangeable spindle head, the machine body having four fixation members whose ends are provided with grooves for the engagement of aligning noses positioned on the rear surface of the spindle head, the fixation members being generally arranged along the coordinates of a coordinate system which intersect on the spindle axes. The fixation members are displaceable along oblique paths so that the setting angle of the milling tools may be changed by a controlled movement of the fixation members. No firm guide surfaces are provided at the carrier body thus not allowing a precise alignment of the interchangeable element with respect to the carrier body.
It is an object of the invention to provide a centering and chucking system in which the reference axes of both elements, also in case of thermal length changes of one element, are not mutually displaced so that a high precision of mutual alignment of both reference axes is not only established, but may be also maintained under varying operating conditions.